The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Nano-positioning apparatuses have been utilized in a variety of applications, such as micro-scale and nano-scale manipulation devices, scanning electron microscope (SEM), scanning probe microscope (SPM), nano-optic technology, nano-robots, and other micro-scale and nano-scale manufacturing or assembling devices.
One prior art nano-positioning apparatus includes a sample platform that supports a sample thereon and an actuating apparatus connected to the sample platform to move the platform. The platform is first coarsely positioned by a coarse positioning mechanism and later finely positioned in nano-scale by the actuating apparatus.
Referring to FIG. 1A, a prior art single-axis actuating apparatus 1 for a nano-positioning apparatus includes a piezoelectric (PZT) actuator 11, a guiding rod 12, and a movable element 13, which are mounted to a housing 14. The guiding rod 12 functions as a driving element to drive the movable element 13 and is slidably and frictionally engaged to movable element 13. The opposing ends of the guiding rod 12 are attached to membrane F1 and F2. The guiding rod 12 is connected to the PZT actuator 11 through the membrane F1. The PZT actuator 11 elongates or contracts in response to an electrical signal, such as voltage, applied to the PZT actuator.
As shown in FIG. 1B, when a voltage is applied to the PZT actuator to make the PZT actuator 11 elongate in a fast speed, the guiding rod 12 is moved by the PZT actuator 11 in the same direction to have a displacement ΔX1. The linear movement of the guiding rod 12, however, does not cause the movable element 13 to move due to inertia of the movable element 13. The movable element 13 remains in the initial position P1. As shown in FIG. 1C, when the voltage applied to the PZT actuator 11 is gradually decreased to zero, the PZT actuator 11 contracts slowly to the initial non-deformed state and moves the guiding rod 12 back to the initial position. When the guiding rod 12 moves, the movable element 13 that is slidably and frictionally engaged to the guiding rod 12 is moved along with the guiding rod 12 due to static friction between the guiding rod 12 and the movable element 13. As a result, the movable element 13 is moved toward the PZT actuator 11 to have a displacement ΔX2. Therefore, the prior art single-axis actuating apparatus 1 uses the “stick-slip phenomenon” to control movement of the movable element and consequently the movement of the sample platform. The “stick-slip phenomenon” has been described in U.S. Pat. No. 7,196,454 and U.S. Pat. No. 5,912,527.
The prior art actuating apparatus 1 controls movement of the platform only in one direction. To move the platform in three dimensions, three single-axis actuating apparatuses 1 are stacked one above the other to form a multi-axis actuating apparatus, called a serial XYZ actuating apparatus. In the serial XYZ actuating apparatus, Z-axis actuating device is placed on top of X-axis actuating device, which in turn is placed on top of the Y-axis actuating device. For nano-scale positioning, stiffness of the actuating apparatus is critical to the ability to resist vibration to ensure high positioning stability and accuracy. The stacked structure of the serial XYZ actuating apparatus requires higher stiffness than a single-axis actuating apparatus, thereby increasing manufacturing costs.
Moreover, an actuating apparatus carrying a higher load is generally operated at a narrower working bandwidth (i.e., lower moving speed). Therefore, the operating speed of the serial XYZ actuating apparatus is adversely affected.